#!/usr/bin/env bash
# Summary: Rehash pyenv shims (run this after installing executables)

set -e
[ -n "$PYENV_DEBUG" ] && set -x

SHIM_PATH="${PYENV_ROOT}/shims"
PROTOTYPE_SHIM_PATH="${SHIM_PATH}/.pyenv-shim"

# Create the shims directory if it doesn't already exist.
mkdir -p "$SHIM_PATH"

acquire_lock() {
  # Ensure only one instance of pyenv-rehash is running at a time by
  # setting the shell's `noclobber` option and attempting to write to
  # the prototype shim file. If the file already exists, print a warning
  # to stderr and exit with a non-zero status.
  local ret
  set -o noclobber
  echo > "$PROTOTYPE_SHIM_PATH" 2>| /dev/null || ret=1
  set +o noclobber
  [ -z "${ret}" ]
}

# If we were able to obtain a lock, register a trap to clean up the
# prototype shim when the process exits.
trap release_lock EXIT

remove_prototype_shim() {
  rm -f "$PROTOTYPE_SHIM_PATH"
}

release_lock() {
  remove_prototype_shim
}

if [ ! -w "$SHIM_PATH" ]; then
  echo "pyenv: cannot rehash: $SHIM_PATH isn't writable"
  exit 1
fi

unset acquired
for (( i=1; i<="${PYENV_REHASH_TIMEOUT:-60}"; i++ )); do
  if acquire_lock 2>/dev/null; then
    acquired=1
    break
  else
    # POSIX sleep(1) doesn't provides time precision of subsecond
    sleep 1
  fi
done

if [ -z "${acquired}" ]; then
  echo "pyenv: cannot rehash: $PROTOTYPE_SHIM_PATH exists"
  exit 1
fi

# The prototype shim file is a script that re-execs itself, passing
# its filename and any arguments to `pyenv exec`. This file is
# hard-linked for every executable and then removed. The linking
# technique is fast, uses less disk space than unique files, and also
# serves as a locking mechanism.
create_prototype_shim() {
  cat > "$PROTOTYPE_SHIM_PATH" <<SH
#!/usr/bin/env bash
set -e
[ -n "\$PYENV_DEBUG" ] && set -x

program="\${0##*/}"
if [[ "\$program" = "python"* ]]; then
  for arg; do
    case "\$arg" in
    -c* | -- ) break ;;
    */* )
      if [ -f "\$arg" ]; then
        export PYENV_FILE_ARG="\$arg"
        break
      fi
      ;;
    esac
  done
fi

export PYENV_ROOT="$PYENV_ROOT"
exec "$(command -v pyenv)" exec "\$program" "\$@"
SH
  chmod +x "$PROTOTYPE_SHIM_PATH"
}

# If the contents of the prototype shim file differ from the contents
# of the first shim in the shims directory, assume pyenv has been
# upgraded and the existing shims need to be removed.
remove_outdated_shims() {
  local shim
  for shim in "$SHIM_PATH"/*; do
    if ! diff "$PROTOTYPE_SHIM_PATH" "$shim" >/dev/null 2>&1; then
      rm -f "$SHIM_PATH"/*
    fi
    break
  done
}

# List basenames of executables for every Python version
list_executable_names() {
  local version file
  pyenv-versions --bare --skip-aliases | \
  while read -r version; do
    for file in "${PYENV_ROOT}/versions/${version}/bin/"*; do
      echo "${file##*/}"
    done
  done
}

# The basename of each argument passed to `make_shims` will be
# registered for installation as a shim. In this way, plugins may call
# `make_shims` with a glob to register many shims at once.
make_shims() {
  local file shim
  for file; do
    shim="${file##*/}"
    register_shim "$shim"
  done
}

registered_shims=" "

# Registers the name of a shim to be generated.
register_shim() {
  registered_shims="${registered_shims}${1} "
}

# Install all the shims registered via `make_shims` or `register_shim` directly.
install_registered_shims() {
  local shim file
  for shim in $registered_shims; do
    file="${SHIM_PATH}/${shim}"
    [ -e "$file" ] || cp "$PROTOTYPE_SHIM_PATH" "$file"
  done
}

# Once the registered shims have been installed, we make a second pass
# over the contents of the shims directory. Any file that is present
# in the directory but has not been registered as a shim should be
# removed.
remove_stale_shims() {
  local shim
  for shim in "$SHIM_PATH"/*; do
    if [[ "$registered_shims" != *" ${shim##*/} "* ]]; then
      rm -f "$shim"
    fi
  done
}

shopt -s nullglob

# Create the prototype shim, then register shims for all known
# executables.
create_prototype_shim
remove_outdated_shims
# shellcheck disable=SC2046
make_shims $(list_executable_names | sort -u)


# Allow plugins to register shims.
OLDIFS="$IFS"
IFS=$'\n' scripts=(`pyenv-hooks rehash`)
IFS="$OLDIFS"

for script in "${scripts[@]}"; do
  source "$script"
done

install_registered_shims
remove_stale_shims
